Actually I remember talking about this with some people and while this is unconfirmed I will still through it out there. I think that Sidious used Juyo. Why?
Well in the RotS Video game each character, and by extension style, has a specific way to hold their lightsaber in defensive mode, Obi-Wan (form III) is right in front of him, exactly like it is in AotC when he faces Dooku. Dooku (form II) is out to the side (hard to explain), but again, exactly how it is in AotC when he does his formal salute to Yoda. Anakin (form V) has his blade hanging over his shoulder, exactly like it is in RotS when he kills the seperatist leaders. Mace (form VII) has his by his right shoulder, pointing forward, but slightly down. Exactly the same as it is in RotS when he faces Sidious. Why is this important? Well Sidious also puts his lightsaber in exactly the same way when he faces both Mace and Yoda.
This can also provide another reason as to why Mace beat Sidious, Mace used the complete form while Sidious was only using an imcomplete form which Mace had mastered to the highest degree.
Also, this was the form that Maul used, since he would have been taught by Sidious, this makes it likely that Sidious also knew Maul. Also, since it takes years to master one form (I remember hearing somewhere that it took 50 years for Dooku to master form II), it is unlikely that Sidious could have mastered two forms, so he probably taught his style to Maul.
And this would not be a bad form for the sith, it is good against both blasters and lightsabers. Plus it does/can draw upon the darkside, making it good for the sith.
Also, Juyo does use jumping movements, combined with strong blows, really exactly how we see Sidious fight in RotS.
So while I have no actual proof, these things lead up to me thinking that Sidious uses Juyo